JPH09228869A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To activate catalysts in art early stage, and concurrently make the difference in output small between each rich cylinder and each lean cylinder by detecting the warming condition of catalysts, setting the quantity of fuel to be fed to specified cylinders when catalysts are in a cooling condition, greater than that to be fed to the other cylinders, furthermore dividing the quantity of fuel, and thereby injecting it thereafter. SOLUTION: While an internal combustion engine is in operation, output signals from an air flow meter 2, a cooling water temperature sensor 5, a crank angle sensor 6 and the like are inputted into a control unit 7, and the quantity of fuel injection to be met to operational conditions is operated so as to be injected-out of each injector 10. In this case, an air-fuel ratio is also detected by an O2 sensor 12 so as to allow feed-back control be executed. Furthermore, the quantity of fuel correction for rich cylinders (specified cylinders) is set much more than the quantity of fuel correction for lean cylinders (other cylinders) in response to water temperature when catalysts are in a cooling condition, concurrently the quantities of ignition timing corrections for the rich cylinders and the lean cylinders have been read in respectively, after the quantity of fuel correction has been made for the rich cylinders, the quantity of fuel injection is divided into a number of several injection times by a specified pulse width so as to be injected there-after.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an internal combustion engine, and more specifically, in order to shorten the catalyst temperature rising period when the engine is cold, the air-fuel ratio of a specific cylinder is made rich and the other cylinders are made lean. The present invention relates to an air-fuel ratio control device having a means for controlling.

[0002]

2. Description of the Related Art As a conventional air-fuel ratio control system for an internal combustion engine, for example, Japanese Patent Application Laid-Open No. 19627/1990 has been disclosed as shown in FIG. The three-way catalyst used for exhaust gas purification is generally activated when the temperature exceeds a certain temperature. Since the catalyst temperature is low during engine cooling, sufficient effect cannot be exhibited until the activation temperature is reached. However, in this case, when unburned components (HC, CO) and oxygen are supplied to the catalyst, the oxidation reaction is promoted and the catalyst can be activated quickly. Further, normally, in order to ensure operability during engine cooling, the air-fuel ratio is set to be richer than the theoretical mixing ratio, and the concentration of unburned components supplied to the catalyst is high, but the concentration of oxygen is generally low. In the conventional example, when the engine is cold, the fuel injection amount in a specific cylinder is reduced to supply high concentration oxygen in addition to unburned components to the catalyst to rapidly activate the catalyst.

[0003]

In such a conventional air-fuel ratio control apparatus for an internal combustion engine, since the air-fuel ratio difference is provided between the cylinders, the cylinder in which the air-fuel ratio is set to rich is selected. On the other hand, in the cylinder set to lean, the output is low, and as a result, there is a problem that torque fluctuation occurs and the drivability deteriorates.

As a means for reducing the torque fluctuation due to the variation of the air-fuel ratio, a method of retarding the ignition timing of the rich cylinder is generally used. However, if the ignition timing is retarded too much even if rich, the combustion cycle There is a limit to the air-fuel ratio difference that can be absorbed because of the large fluctuation. In the above-mentioned conventional example, the larger the air-fuel ratio difference between the cylinders is set, the larger the obtained catalyst activation promoting effect becomes, and in this case, the ignition timing control alone cannot absorb the output difference between the cylinders.

The present invention has been made by paying attention to such a conventional problem. In order to accelerate catalyst activation during engine cooling, the air-fuel ratio of a specific cylinder is made rich and the other cylinders are made lean. At this time, the fuel injection pulse width TpR of the rich cylinder is divided into a plurality of times to supply the fuel spray having a large particle size at the initial stage of the injection to the H level.
An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can reduce the rich degree by generating a large amount of C and CO and reduce the output difference between the rich cylinder and the lean cylinder.

[0006]

In order to solve the above problems, the present invention provides an air-fuel ratio control system for an internal combustion engine according to claim 1, wherein the fuel supplied to a specific cylinder when the catalyst is in a cold state. When the fuel amount is set to be larger than that of the other cylinders, the fuel amount is divided into a predetermined pulse width and injected. That is, as shown in FIG. 1, a catalyst warm-up state detecting means a for detecting a catalyst warm-up state, and a fuel for setting the amount of fuel supplied to a specific cylinder when the catalyst is in a cold state to be larger than those of other cylinders. An amount setting means b and a fuel injection dividing means c for dividing the fuel amount into a predetermined pulse width and injecting the fuel with a fuel injection valve d are provided.

Further, in the air-fuel ratio control apparatus for an internal combustion engine according to claim 2, when the amount of fuel supplied to a specific cylinder is set to be larger than that of other cylinders when the catalyst is in a cold state, this fuel amount is set to a predetermined pulse. A means for starting the fuel injection so that the fuel injection ends at the set injection end timing is provided. That is, as shown in FIG. 2, catalyst warm-up state detection means a for detecting the warm-up state of the catalyst, and fuel for setting the amount of fuel supplied to a specific cylinder when the catalyst is in the cold state to a value larger than that of other cylinders An amount setting means b, an injection number calculating means e for calculating the number of injections required to inject this fuel amount based on a predetermined pulse width, an injection end timing setting means f for setting the fuel injection end timing, An injection start timing setting means g is provided for setting the injection start timing based on a predetermined pulse width and the number of injections so that the injection is ended at the injection end timing.

Further, in the air-fuel ratio control device for an internal combustion engine according to claim 3, the predetermined pulse width according to claims 1 and 2 is set to the minimum pulse width that can set the fuel injection valve d.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment) FIG. 3 is a diagram showing a configuration of an air-fuel ratio control apparatus for an internal combustion engine according to an embodiment of the present invention.

In FIG. 3, an air flow meter 2 is provided downstream of an air cleaner 1 provided at the uppermost stream of the intake air passage to measure the flow rate of intake air. The throttle valve 3 provided downstream of the throttle valve 3 has a throttle opening sensor 4
Is provided to measure the throttle opening. These measurement results are sent to the control unit 7 together with information on the operating state of the engine, that is, the output of the cooling water temperature sensor 5 and the output of the crank angle sensor 6. The control unit 7 calculates the fuel injection amount according to the operating state, and injects fuel from the injector 8 provided in the intake manifold 9 branched from the collector 8 for each cylinder.

Further, an O ₂ sensor 12 is provided at the collecting portion of the exhaust manifold 11 to detect the air-fuel ratio of the exhaust gas. The detection result is sent to the control unit 7, and after the engine is warmed up, the air-fuel ratio feedback control is performed based on the detection result. The control unit 7 also calculates the ignition timing according to the operating state, and the ignition plug 13 ignites each cylinder based on the result.

Next, the operation will be described.

FIG. 4 shows a flowchart for calculating the fuel injection amount and the ignition timing. First, in step S1, engine speed Ne, air flow meter output Qa, water temperature sensor output Tw
Read. In the next step S2, the basic fuel injection amount Tp
= K × Qa / Ne (K: constant) is calculated, and the basic ignition advance value ADV is searched from the Tp-Ne map. In the next step S3, it is determined whether or not the water temperature Tw is lower than a predetermined value Tw1, and if it is lower, it is determined that the engine is in a cold state and the process proceeds to step S4. On the other hand, when Tw is higher than Tw1, that is, when it is determined that the engine has been warmed up, the process proceeds to step S9, and air-fuel ratio feedback control is performed to correct the fuel injection amount based on the O ₂ sensor output. The details of the air-fuel ratio feedback control are the same as the conventional ones, and thus the description thereof is omitted.

By the way, in step S4, the fuel correction amount kt of the rich cylinder (specific cylinder) according to the water temperature Tw from FIG.
wR, the fuel correction amount ktwL of the lean cylinder (other cylinder) is read, and the fuel correction amounts ktwR and ktw are read from FIG.
Ignition timing correction amount advtw of the rich cylinder according to L
The ignition timing correction amounts advtwL for the R and lean cylinders are read, and the injection amount and the ignition timing are corrected in accordance with them in the next step S5. Next, in step S6, the number of times n for injecting the corrected fuel injection amount TpR of the rich cylinder in a plurality of times with a predetermined pulse width Tpr is TpR = Tpr.
Calculate from xn.

At step S7, each predetermined pulse width T
The interval of pr is set to the valve closing delay time Tb of the injection valve with respect to the drive pulse shown in FIG. 7 so that the set injection end timing is reached.
The signal shown in FIG. 8 is sent to the injector. Thus, in the rich cylinder, the concentration of unburned components in the exhaust is increased to be richer than the stoichiometric air-fuel ratio, while in the lean cylinder, the oxygen concentration in the exhaust is increased to be leaner than the stoichiometric air-fuel ratio. At this time, the ignition timing is set to retard the stability limit of each of the rich cylinder and the lean cylinder, and the exhaust temperature is increased to accelerate the activation of the catalyst together with the air-fuel ratio control.

Therefore, when the specific cylinder is made richer than the other cylinders for early activation of the catalyst when the engine is cold, the fuel injection pulse width of the rich cylinder is injected by dividing the fuel injection pulse width into a plurality of predetermined pulse widths. As a result, a fuel spray having a large particle size at the initial stage of injection is supplied, which deteriorates combustion and causes unburned components (H
Since the composition is such that a large amount of C, CO) is generated, the oxidation reaction in the catalyst is promoted, and the catalyst is quickly activated. Therefore, as compared with the conventional control, the rich degree of the rich cylinder can be reduced as shown in FIG. 9, the output difference between the rich cylinder and the lean cylinder can be reduced, and the rebound to the drivability can be reduced.

(Second Embodiment) The configuration of this embodiment is the same as that of the first embodiment, and therefore the description thereof is omitted.

Next, the operation will be described.

In this embodiment, the predetermined pulse width Tpr in the first embodiment is set as the settable minimum pulse width Tpmin of the injection valve. As shown in FIG. 7, the fuel injection valve has a delay in operation with respect to the drive signal, so that there is a minimum effective drive signal width (settable minimum pulse width Tpmin) peculiar to the fuel injection valve. By using this Tpmin, the number of divisions of the fuel injection pulse width, that is, T
The number of injections at pr (= Tpmin) is maximized, and the spray having the largest particle size at the initial stage of injection is supplied most.

Therefore, when the specific cylinder is made richer than the other cylinders for early activation of the catalyst when the engine is cold, the fuel injection pulse width of the rich cylinder is injected by dividing the fuel injection pulse width into a plurality of predetermined pulse widths. , The predetermined pulse width is set as the minimum pulse width that can be set by the injection valve, thereby maximizing the number of injections, supplying a larger amount of fuel spray having a large particle size in the initial stage of injection, and deteriorating combustion, resulting in unburned components (HC, Since a large amount of CO) is generated, the oxidation reaction in the catalyst is further promoted, and the rich degree of the rich cylinder can be reduced as shown in FIG. 9 as compared with the conventional control, and the output difference between the rich cylinder and the lean cylinder is small. Therefore, the rebound to the drivability can be reduced.

[0022]

As described above, according to the first aspect of the invention, the fuel amount setting means b is provided for early activation of the catalyst when the catalyst is in the cold state judged by the catalyst warm-up state detecting means a. Accordingly, when the specific cylinder is made richer than the other cylinders, the fuel injection dividing means c outputs a command to the fuel injection valve d to inject the fuel injection pulse width of the specific cylinder at a predetermined pulse width in plural times. Therefore, a large amount of fuel spray having a large particle size at the initial stage of injection is supplied, the fuel spray having a large particle size is difficult to vaporize, and the mixture with air is poor and the combustion state is poor, so that unburned components (HC, CO) Since it is configured to generate a large amount of catalyst, early activation of the catalyst can be obtained, while the rich degree of the rich cylinder can be reduced compared to the conventional control, the output difference between the rich cylinder and the lean cylinder can be reduced, and the rebound to the drivability can be reduced. In reduction That.

According to the second aspect of the present invention, when the catalyst is warmed down as judged by the catalyst warm-up state detecting means a, the fuel amount setting means b is used to change the specific cylinder to another cylinder for early activation of the catalyst. Is output to the injection number calculation means e, and the injection number calculation means e calculates the number of times of injection by dividing the fuel injection pulse width of the specific cylinder into a predetermined pulse width, and the output and fuel injection In response to the output from the injection end timing setting means f for setting the end timing, the injection start timing setting means g outputs a command to start the injection to the fuel injection valve d so that the injection ends at the injection end timing. Because of the configuration, the fuel required for the control to start the fuel injection divided into a plurality of times can be sucked into the combustion chamber so that the injection ends at the set injection end timing.

Further, according to the invention of claim 3, the predetermined pulse width of claims 1 and 2 is set as the minimum pulse width that can be set for the fuel injection valve, and the number of injections in one cycle is maximized. Since the fuel spray having a large diameter is supplied more, the fuel spray having a large particle diameter is difficult to vaporize, and the mixing with air is poor and the combustion state is bad, the unburned components (HC, C
O) is generated in a large amount, so that it is possible to generate a larger amount of unburned components by controlling the fuel injection pulse width of the rich cylinder to be injected by dividing the fuel injection pulse width into the minimum settable fuel injection pulse width of the injection valve. , The activity of the catalyst is further promoted.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an air-fuel ratio control device for an internal combustion engine of the present invention.

FIG. 2 is a configuration diagram of an air-fuel ratio control device for an internal combustion engine of the present invention.

FIG. 3 is a configuration diagram according to the first embodiment of the present invention.

FIG. 4 is a flowchart showing an operation of the first exemplary embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between a water temperature Tw and fuel correction factors ktwR and ktwL in the embodiment of the present invention.

FIG. 6 is a fuel correction rate ktw according to the embodiment of the present invention.
R, ktwL and ignition timing correction amount advtwR, advt
It is a figure which shows the relationship of wL.

FIG. 7 is a diagram showing drive pulses and actual movements of the fuel injection valve according to the embodiment of the present invention.

FIG. 8 is a diagram showing a fuel injection pulse width in the embodiment of the present invention.

FIG. 9 is a diagram showing an air-fuel ratio of each cylinder in the embodiment of the present invention.

FIG. 10 is a diagram illustrating conventional air-fuel ratio control.

[Explanation of symbols]

a catalyst warm-up state detecting means b fuel amount setting means c fuel injection dividing means d fuel injection valve e injection number calculating means f injection end timing setting means g injection start timing setting means 1 air cleaner 2 air flow meter 3 throttle valve 4 throttle opening Sensor 5 Cooling water temperature sensor 6 Crank angle sensor 7 Control unit 8 Collector 9 Intake manifold 10 Injector 11 Exhaust manifold 12 O ₂ sensor 13 Spark plug

Claims (3)

[Claims] 1. A catalyst warm-up state detecting means for detecting a warm-up state of a catalyst, and a fuel amount setting means for setting a fuel amount supplied to a specific cylinder when the catalyst is in a cold state to be larger than those of other cylinders. An air-fuel ratio control apparatus for an internal combustion engine, comprising: a fuel injection dividing unit that divides the fuel amount into a predetermined pulse width and injects the divided fuel into a predetermined pulse width. 2. An injection number calculation means for calculating the number of injections required to inject the fuel amount based on a predetermined pulse width, an injection end timing setting means for setting an injection end timing of the fuel, and an injection end timing. 2. An injection start timing setting means for setting an injection start timing based on a predetermined pulse width and the number of injections so that the injection is completed.
An air-fuel ratio control device for an internal combustion engine according to the above. 3. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the predetermined pulse width is a minimum pulse width that can be set for the fuel injection valve.